[PATCH RFC 01/16] fs: record sequence number of origin mount namespace

[Christian Brauner <brauner@kernel.org>]

Store the sequence number of the mount namespace the anonymous mount
namespace has been created from. This information will be used in
follow-up patches.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/mount.h     |  1 +
 fs/namespace.c | 17 +++++++++++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/mount.h b/fs/mount.h
index ffb613cdfeee..820a79f1f735 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -20,6 +20,7 @@ struct mnt_namespace {
 		wait_queue_head_t	poll;
 		struct rcu_head		mnt_ns_rcu;
 	};
+	u64			seq_origin; /* Sequence number of origin mount namespace */
 	u64 event;
 	unsigned int		nr_mounts; /* # of mounts in the namespace */
 	unsigned int		pending_mounts;
diff --git a/fs/namespace.c b/fs/namespace.c
index a3ed3f2980cb..9bcfb405b02b 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2853,15 +2853,28 @@ static int do_loopback(struct path *path, const char *old_name,
 
 static struct file *open_detached_copy(struct path *path, bool recursive)
 {
-	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
-	struct mnt_namespace *ns = alloc_mnt_ns(user_ns, true);
+	struct mnt_namespace *ns, *mnt_ns = current->nsproxy->mnt_ns, *src_mnt_ns;
+	struct user_namespace *user_ns = mnt_ns->user_ns;
 	struct mount *mnt, *p;
 	struct file *file;
 
+	ns = alloc_mnt_ns(user_ns, true);
 	if (IS_ERR(ns))
 		return ERR_CAST(ns);
 
 	namespace_lock();
+
+	/*
+	 * Record the sequence number of the source mount namespace.
+	 * This needs to hold namespace_sem to ensure that the mount
+	 * doesn't get attached.
+	 */
+	src_mnt_ns = real_mount(path->mnt)->mnt_ns;
+	if (is_anon_ns(src_mnt_ns))
+		ns->seq_origin = src_mnt_ns->seq_origin;
+	else
+		ns->seq_origin = src_mnt_ns->seq;
+
 	mnt = __do_loopback(path, recursive);
 	if (IS_ERR(mnt)) {
 		namespace_unlock();

-- 
2.47.2